PRACTICAL ORGANIC CHEMISTRY
Quantitative Hydrolysis of Ethyl Benzoate.The
quantitative estimation of an ester by hydrolysis is conducted as
follows : a standard half-normal solution of alcoholic potash is
prepared by dissolving 7 grams of caustic potash in about an
equal weight of water and diluting to 250 c.c. with absolute
alcohol. The liquid is allowed to stand overnight in a stoppered
flask and filtered through asbestos
into a clean diy bottle closed with a
cork through which a 25 c.c. pipette
is inserted. The solution is first
standardised by titration against half-
normal sulphuric acid, using phenol-
phthalein as indicator. About I gram
of ethyl benzoate is carefully weighed
by difference by means of the ap-
paratus shown in Fig. 82.
A volume corresponding to about
I gram is delivered into a- round
flask (200 c.c.) by attaching a piece of rubber tubing to the wide
end of the apparatus and blowing until the liquid descends to
the required graduation on the wide limb. Twenty-five c.c. of the
standard alcoholic potash solution is added, and the mixture
boiled on the water-bath with reflux condenser for twenty
The amount of free alkali is estimated by titration with
standard sulphuric acid and the quantity of ester calculated.
Example.1'355 grams required 15'! c. c. N/2H2S04
15-1 XQ-I50X 100
See Appendix^ p. 308.
" = 997 per cent.
ff Acetophenone (Phenylmethylketone, Hypnone),
Friedel, Crafts, Ann. Chim. Phys., 1884, 1, 507 ; 14, 455.
30 grms. benzene.
50 aluminium chloride (anhydrous).
35 acetyl chloride.